1. Field of the Invention
This invention relates to heating, venting and air conditioning (HVAC) and refrigeration systems, and more particularly, to a device for controlling the flow of fluids in HVAC and refrigeration systems.
2. Description of Related Art
This invention relates to HVAC and refrigeration systems, and in particular to a device for maximizing the efficiency of working fluids in a refrigeration system. While the invention is described in detail with respect to a conventional refrigeration or HVAC system, those skilled in the art will recognize the wider applicability of the invention disclosed hereinafter. The invention may find application, with other refrigeration systems where system efficiency may be improved by monitoring specific parameters affecting that efficiency.
The operational features of conventional refrigeration systems are well known in the art. An example of such a system is a refrigerated container, such as a supermarket display case. In general, the refrigeration system would include a compressor that forces the particular refrigerant used in the system through a condensing coil, where the refrigerant vapor liquefies. The liquid refrigerant passes through a thermostatic expansion valve, expanding the high pressure liquid refrigerant to a low pressure vapor. The low pressure, low temperature refrigerant discharged from the thermostatic expansion valve is then directed through an evaporator coil for absorbing heat and thus refrigerating the space inside the container surrounding the evaporator coil.
The thermostatic expansion valve meters the flow of refrigerant into the evaporator coil in proportion to the rate of evaporation of the refrigerant in the evaporator coil, and is responsive to the temperature and pressure of the refrigerant leaving the evaporator coil. In this manner, the thermostatic expansion valve can control the refrigerant leaving the evaporator coil at a predetermined superheat. Generally, the superheat of the refrigerant is a measure of the heat contained in the refrigerant vapor above its heat content at the boiling point (saturated vapor temperature) at the existing pressure. Maintaining the refrigerant entering the suction line from the evaporator coil at a desired superheat level enhances the refrigeration system performance.
Thermal expansion valves, however, control only to a specific refrigerant superheat. Any changes in the system resulting in a change in evaporator coil pressure also cause a corresponding change in the display case temperature--even with the same superheat. In order to provide more consistent case temperature, a suction regulator may be used to maintain a consistent evaporator coil pressure. In known systems, conventionally designed mechanical pressure regulators are used for this purpose. Conventional mechanical pressure regulators include a throttling element that, when moved, limits the flow of the refrigerant through the suction regulator to regulate the pressure. A diaphragm, or other sensing element, responds to variations in the inlet pressure and moves the throttling element accordingly. A reference pressure, typically exerted by a spring, is applied to one side of the diaphragm to bias the diaphragm in a desired position, or set point. High side inlet pressure is applied to the other side of the diaphragm to move the diaphragm against the spring, and thus, move the throttling element.
Adjusting the set point requires a time consuming, manual process. Once the regulator's bias spring is adjusted for the proper set point, case temperature control can be expected to be plus or minus about 4.degree. F. In many refrigeration system implementations, finer temperature control is desirable. With the example grocery store case refrigeration system, several factors fuel the need for finer case temperature control. Government regulations may require more stringent temperature regulation, and requirements for longer product shelf life and improved product quality further make tighter control of case temperature a necessity. Moreover, if the refrigerant or desired temperature changes, the complicated process of manually adjusting the pressure regulator's set screw must be repeated.
The present invention addresses these, and other, shortcomings associated with the prior art.